Bulb



FIG. 1 is a front perspective view of the design, the portion shown in shadow lines not forming part of the design;

FIG. 2 is a side elevation view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof; and,

FIG. 5 is a front perspective view of an alternate embodiment thereof, the portion shown in shadow lines not forming part of the design. 

The ornamental design for a bulb, as shown and described. 